This message is to all of you who have downloaded my educational CFD shareware MicroTunnel in the past:

One of the major complaints has always been that the program was running at snail's pace, especially at higher resolutions, so I finally decided to fix that. The inviscid flow solver, based on Van Leer's flux vector split scheme, has been converted to a DLL written in assembly language. Together with a few minor algorithm improvements, all aerodynamic simulations, whether subsonic, transonic or supersonic, now run six times faster. The flow solver is still explicit, and no convergence acceleration of any kind has been implemented. Following the unsteady development or character of a flow is part of the educational experience. (See www.cfd4pc.com/prism.htm for an unsteady simulation).

Further, I decided to fix the tunnel resolution to 800x600 (maximum), which made memory addressing a lot more efficient from a machine viewpoint. This became evident when I started writing the assembly code. Since the output display is 800x600, this means that one pixel on the display corresponds to exactly one finite volume cell in the flow. I call it a 'photographic' solution.

I am still planning to improve the surface boundary routine using a more advanced 'cut-cell' technique. Right now things are simply Cartesian (jagged surface), which does have some interesting effects though. One can get separated (recirculating) flow over blunt bodies or airfoils at high angle of attack although the flow solver is purely inviscid. Again, numerical viscosity is always present, which is why you see some of these wake effects.

Whether or not you have downloaded MicroTunnel in the past, the new version (1.2) comes with another two-week trial period. No pre-registration is necessary. The download is free, and it is the full version. Just go to,

I have tested the installation program on a number of different Windows platforms and did not run into any glitches. If someone should have a problem with the installation, please let me know right away!

Any questions, comments, or suggestions are always appreciated. Again, keep in mind that this shareware is intended purely for educational purposes (only $30 for a permanent license), so don't throw away your Fluent package just yet...